In a traditional dryer shown in FIG. 1, clothes are placed in a rotating tumbler. Air from the outside is drawn in, heated, circulated through the tumbler and vented outside.
Even though the basic design is simple, reliable, and cheap, the high operating temperature (about 180 F) causes lint to form and clothes to shrink. In addition, this basic design requires venting ducts to the outside to prevent the buildup of high indoor humidity. It is inherently inefficient because no attempt is made to recycle the heat that is applied to the laundry load.
Just as in a traditional dryer, a condenser dryer illustrated in FIG. 2 requires that heated air pass through the load. However, instead of venting this air outside, the dryer uses a heat exchanger to cool the air and condense the water vapor. After the water is extracted, the air is heated and goes through the loop again. The heat exchanger uses as its coolant, ambient air which is vented in the immediate surroundings; alternatively it may use cold water, resulting in increased water usage.
Even though condenser dryers are “closed loop” requiring no venting of the humid air from the laundry, they do not recycle heat energy and their heat exchangers still dump heat in the environment. They are about 15% less efficient than conventional clothes dryers because of inefficiency introduced by the heat exchanger.
In a heat pump dryer shown in FIG. 3 heat energy is recycled. The same heat pump is used simultaneously to cool the air leaving the tumbler and to heat the air entering the tumbler. Such dryers not only avoid the need for ducting, but also conserve much of their heat within the dryer instead of exhausting it into the surroundings. Heat pump dryers can therefore use less than half the energy required by either condensation or traditional dryers.
Disadvantages of heat pump dryers include their need for two heat exchangers and their reliance on hydrochlorofluorocarbon (HCFCs) refrigerant fluids such as R-22 or R-134a. These fluids have been shown to be 2000 times more powerful than carbon dioxide at causing global warming. Their predecessors, the Chlorofluorocarbons (CFCs) such as Freon™, were banned because of their deleterious effect on the ozone layer. There is therefore a strong incentive to eliminate these chemicals from devices using a heat pump such as clothes dryers and, air conditioners. The proposed technology is an improvement to, and is more efficient, simple, compact and environmentally friendly than, the heat pump dryer.
Vacuum dryers are the subject of numerous patents. However, very little of this technology has reached the market because of their slow drying speed. Little consideration is given in the prior art to how the heat flows: as water evaporates, heat of vaporization is provided by the clothes which get colder, slowing down the evaporation process. Heating the clothes, a possible solution, is inefficient and does not address the issue of recycling the heat energy. Another problem is their need for a strong sealed vacuum chamber to enclose the tumbler and the possibility of implosion should this chamber fail.
Microwave dryers operate around 2.45 GHz. At this frequency microwaves have the interesting property of being selectively absorbed by water and are appropriate for food items. Unfortunately the presence of metal in clothing could result in sparking and fires, making microwaves unacceptable for laundry applications. No clothes dryer described in the prior art, however, offers the economy, reliability, efficiency and environment sustainability of the present invention. Further features, aspects, and advantages of the present invention over the prior art will be more fully understood when considered with respect to the following detailed description and claims.